Will these fit my current wheels without removing the old lug nuts?

These are a direct swap for any M12 x 1.5 stud — unthread the old nuts and thread these on. No wheel removal necessary unless you want to clean behind them.

Do I need to do anything to the finish before installation?

The anodized finish ships ready to install. Just clean your studs if there's visible rust or debris, then thread them on hand-tight first, then torque to your vehicle's spec.

Are these enough for a full set on a five-lug truck?

Twenty nuts cover four vehicles at five lugs per wheel, or five vehicles at four lugs per wheel. If you're doing a single vehicle, you'll have spares — that's intentional insurance.